Spacecraft perform various maneuvers after they are launched into space and once they are on-station in an intended orbit. After the spacecraft is on-station in a selected orbit, various forces (e.g., solar and/or other environmental disturbance torques, such as magnetic torques) may act on the spacecraft and cause the spacecraft to drift away from its selected orbit into another, incorrect orbit. Thus, periodic (e.g., daily, weekly, or monthly) orbital maneuvers are often required to return the spacecraft to the correct orbit. These types of maneuvers are known as station-keeping maneuvers.
It is also required to correctly orient a spacecraft having solar panels with the sun, in order to maximize the generation of electrical power.
During the performance of such maneuvers the precise control of the spacecraft's attitude to orient the spacecraft's payload, such as communication or imaging hardware, to a preselected planetary location and/or to correctly orient the spacecraft's thrust vector is also important. Thus, spacecraft are typically equipped with closed-loop control systems which enable the attitude of the spacecraft to be controlled within pre-established deadband limits. Such control systems often employ spacecraft thrusters for selectively producing torques on the spacecraft for correcting and maintaining the spacecraft attitude.
The following commonly assigned U.S. patents are illustrative of various approaches to providing spacecraft attitude control: U.S. Pat. No. 5,459,669, Control System And Method For Spacecraft Attitude Control, to Adsit et al.; U.S. Pat. No. 5,400,252, Spacecraft East/West Orbit Control During A North Or South Stationkeeping Maneuver, to Kazimi et al.; U.S. Pat. No. 5,349,532, Spacecraft Attitude Control And Momentum Unloading Using Gimballed And Throttled Thrusters, to Tilley et al.; and U.S. Pat. No. 5,222,023, Compensated Transition For Spacecraft Attitude Control, to Liu et al.
Reference can also be had to U.S. Pat. No. 5,184,790, Two-Axis Attitude Correction For Orbit Inclination, to Fowell; U.S. Pat. No. 4,931,942, Transition Control System For Spacecraft Attitude Control, to Garg et al.; U.S. Pat. No. 4,848,706, Spacecraft Attitude Control Using Coupled Thrusters, Garg et al.; U.S. Pat. No. 4,767,084, Autonomous Stationkeeping For Three-Axis Stabilized Spacecraft, to Chan et al.; U.S. Pat. No. 4,599,697, Digital PWPF Three Axis Spacecraft Attitude Control, to Chan et al.; U.S. Pat. No. 4,521,855, Electronic On-Orbit Roll/Yaw Satellite Control, to Lehner et al.; U.S. Pat. No. 4,489,383, Closed-Loop Magnetic Roll/Yaw Control System For High Inclination Orbit Satellites, to Schmidt, Jr.; and U.S. Pat. No. 4,084,772, Roll/Yaw Body Steering For Momentum Biased Spacecraft, to Muhlfelder. Also of interest is U.S. Pat. No. 4,759,517, Station-Keeping Using Solar Sailing, to Clark; and U.S. Pat. No. 4,684,084, Spacecraft Structure with Symmetrical Mass Center and Asymmetrical Deployable Appendages, to Fuldner et al.
Reference is also made to a publication entitled "Attitude Stabilization of Flexible Spacecraft During Stationkeeping Maneuvers", Bong Wie et al., J. Guidance, Vol. 7, No. 4, pgs. 430-436, July-August 1984.
The use of quaternion feedback for large angle reorientation maneuvers using reaction jets is discussed in a publication entitled "Quaternion Feedback for Spacecraft Large Angle Maneuvers", J. Guidance, Vol. 8, No. 3, May, June 1985, pgs. 360-365.
It can be appreciated that a technique to reorient and hold, or to reorient and rotate, a spacecraft along a user specified axis in order to meet power, thermal, telemetry and control mission constraints is an important aspect of spacecraft operation.